1. Field of the Invention
The present invention relates to three-dimensional (3D) object detecting apparatuses and 3D object detecting methods. In particular, the present invention relates to a 3D object detecting apparatus and a 3D object detecting method which are advantageous to detect a 3D object on an image-capture surface on the basis of an image captured by a single image-capture device.
2. Description of the Related Art
Hitherto, a traffic impediment warning system has been known. In some systems, an impediment on a road surface is detected in an image captured using a monocular (a single) camera mounted on a vehicle and the system issues a warning with respect to the detected impediment.
Various 3D-object detecting methods have been applied to such a traffic impediment warning system. One known example is a method disclosed in Japanese Unexamined Patent Application Publication No. 10-222679. In the method (which is the so-called “background differencing method”), an amount of movement of a vehicle is determined and a past image and a current image captured by a monocular camera are compared with each other to eliminate unnecessary regions, such as a road surface and a distant view, and to extract only 3D objects (movable bodies) on the road surface.
In such a 3D-object detecting method, typically, in order to estimate the position of a 3D object on the basis of an image captured by a camera, a position at which the ground side (i.e., the ground contact point) of the 3D object is shown in the captured image is detected.
Thus, in the 3D-object detecting methods of the related art, for a camera fixed to a movable platform, such as a vehicle, how a background other than the 3D object is seen varies as the camera moves, thus making it difficult to appropriately detect only a region showing the 3D object from the image captured by the camera. Consequently, a false positive detection (e.g., detection of an unnecessary background) or a false negative detection (e.g., detection of only part of the 3D object) may occur. Such a false positive detection and false negative detection could occur owing to variations in a sunshine condition, lighting condition, or the like on an image-capture surface (e.g., a road surface or a floor surface), even when the vehicle is stopped or the camera is fixed to a stationary platform (e.g., a building).
For a 3D-object detection image resulting from such a false positive detection or false negative detection, complex processing, such as pattern matching (see, for example, Japanese Unexamined Patent Application Publication Nos. 2010-056975 and 2007-129560), needs to be performed to accurately detect the ground side of the 3D object. Thus, a position accuracy is considerably reduced compared to cases in which no false positive/negative detection occurs. Such a reduction in the position accuracy adversely affects, for example, the precision of determining whether or not the detected 3D object is a stationary object or a movable body and whether or not the detected 3D object is approaching or moving away. The reduction in the position accuracy may thus lead to a decrease in the reliability of the camera-image processing system (e.g., a traffic impediment warning system or a monitoring camera system) employing the 3D-object detection. Accordingly, it is necessary to provide en early solution to such a problem.